It Was Supposed to be a Simple Birthday Present
by Greekgirrl
Summary: All Magnus wanted to do was give his girlfriend a present for her birthday! In hindsight, he probably should have known that giving her something that had once belonged to Henry Branwell wasn't a good idea... Oh, well, what's past is in the past. Or is it? I'm not the best summarizer but please read! :)
1. Chapter 1

Pairings: Magnus/OC, Jace/Clary, Isabel/Simon implied, mention of Alec/Magnus and Magnus/Camille in the past (later)

Disclaimer: I don't own either of these amazing series. Cassandra Clare gets that privilege. Lucky duck! Though, I don't trust the ducks. :3

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**A/N: HI! So, I've been wanting to write an Infernal Device/Mortal Instruments Cross-over forever, but I couldn't come up with a story that inspired me! Then I offered to write a fic for my friend for Christmas and this was born! Here you are symmetricalravenxx8, I hope you enjoy it, honey!**

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"Just a bit longer," Magnus whispered mischievously causing the hairs at the base of Grace Lombard's neck to stir and sending a shiver down her spine.

She squirmed impatiently and whined to him in her posh British accent, "But, Magnus, you've been leading me around with this blindfold on for _hours, _love."

He rolled his eyes at her. While he _had_ insisted that she be blindfolded for the past 30 minutes, it wasn't his fault! She wouldn't leave the apartment even to give him time to set up her birthday party- perhaps it was her aversion to parties thrown for her that led to her being so stubborn, but then again she was stubborn about most things. It was just part of her personality. You see, Grace Lombard was a warlock. She had been alive for centuries now, so many so that she usually couldn't recall her own age. The only thing she could tell you definitively about her age was that she was younger than Magnus. The younger warlock had known him for most of her life seeing as they had been best friends basically since meeting; and because of him, recently she had been introduced to the Shadowhunters of New York on her latest visit with him. With her eccentric yet completely lovable personality, she had fallen in with the Nephilim immediately. She even got along particularly well with Alec Lightwood, Magnus' ex-boyfriend, who had given her his blessing to date Magnus. She remembered the conversation well and with a smile she thought back a few weeks to when it had occurred.

~_Flashback_~

"_Alec, can I tell you something?" Grace asked hesitantly. She knew that this would be a delicate subject with Alec as he still cared for Magnus, but she was unsure whether or not he still loved him._

"_Of course," he replied with a smile and an encouraging nod. Alec had just met Grace a few weeks ago and already they were extremely close; he would even say they were nearing best friends- she was just that kind of person who you could become friends with in an instant and they were both extremely comfortable around each other- so he was curious about her hesitancy._

"_Well, Magnus asked me to go on a date with him today, and I've no clue what to say to him!" she exclaimed nervously twirling some of her light brown hair between her fingers._

"_I don't see why not," he said mildly. Despite Grace's doubts, Alec had fully bounced back from the break-up and wanted nothing more than for his new friend to be happy. "I mean unless you don't feel the same way about him," he said realization coloring his tone. He almost felt bad for Magnus now because Grace really was a very special girl and he could see why any man would want to be with her._

"_I'm just not sure how I feel," she worried anxiously. "And I don't want to give him the wrong idea or lead him on! Magnus is one of my best friends- always has been."_

"_Well, whatever you decide, I want you to know that I am perfectly fine with it. Magnus and I are water under the bridge, so feel free to do what your heart is telling you, regardless of your worries about me," Alec quipped grinning at Grace as he saw right through her to her deeper concerns. She smiled radiantly at him and pulled him into a quick sideways hug before flitting out of the room with a brief, "Thanks, Alec!" yelled over her shoulder._

~_End Flashback_~

Just as Grace surfaced from her memories, Magnus was taking the blindfold off of her eyes and yelling, "Surprise!" along with the Shadowhunters that had become very close friends of hers.

She rolled her eyes at them and said, "Well it isn't really a surprise if I've known about since you started planning it, now is it?" She smirked at them and Magnus shook his head in exasperation while wrapping his arms around her waist.

"Wanna open your presents or not?" Jace asked his ever-present smirk mirroring hers.

She shrugged in acquiescence and took a seat on a huge cushy armchair that Magnus must have conjured up along with the rest of the furniture in his usually empty loft. Said warlock plopped down next to her making her tilt sideways and practically fall across his lap.

"You did that on purpose!" Grace exclaimed trying and failing to sound angry. Magnus simply chuckled at her as sat her back up, leaving his arms around her shoulders.

"Open mine first," he purred quietly handing her an oddly shaped object covered in layers upon layers of wrapping paper. "It was something that I got in London in- jeez, it was a lifetime ago."

She nodded, completely understanding what he meant, but didn't open the present. She just studied it closely, eyeing it suspiciously. "How much wrapping paper did you use on this thing?! You know they have these things called gift bags for all your oddly shaped gift-giving needs," she said laughing at her boyfriend as he frowned at her and pretended to be offended. "It's a good thing I have these then," she teased, letting her claws slide out. They were her mark- instead of cat eyes like Magnus, Ragnor Fell's whole exterior, or claws like the Dark Sister, Mrs. Black- she had retractable claws like a cat. She then drew her index finger along what she discerned was the bottom of the present, effectively slitting the paper all the way to the mysterious object. She then eagerly ripped the rest of the paper off, not bothering to put away the claws.

Once she had unwrapped it, Grace turned her head to the side to closely scrutinize the device in her hands, looking very much like a cat in the process. "What is it?" she inquired perplexedly.

Magnus gave a low laugh at her confusion and proceeded to clarify what exactly the strange _thing _was. "Since I know you do so enjoy the inventions of mortals almost as much as you love music- I said almost!" he exclaimed when she gave him the evil eye for even daring to compare anything to music. "Anyway, since you like that stuff I decided to find something old that maybe you could find some use for or, I don't know, just figure out. This was a component of an invention of Henry's that he never worked out how to get functioning. It was something he started later in life, so he passed before he could see it to completion." The Shadowhunters looked confused, but Grace had been told many times about the Nephilim of the London Institute that Magnus had grown so attached to in the late 19th century.

She started studying the device anew and asked a bit absently, "Do you know what he intended for it to be?"

"I don't know," Magnus admitted with a shrug. He was just glad that Grace liked the present!

"Hmmm, I wonder what this does," she muttered contemplatively, pressing a button on the side of the object after doing some rewiring.

Seemingly out of nowhere, a portal started to expand from the thing dragging all of the occupants of the room into the swirling darkness. Grace, Magnus, Alec, Clary, Jace, and Isabelle were sucked in, taking them God only knows where!

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After what felt like an eternity, they all found themselves sprawled out in a cramped courtyard in front of a huge, castle-like church with towering spires and a wrought-iron gate surrounding the place. Grace rolled over and groaned. While the journey through the portal hadn't hurt per se, it did leave one aching and utterly exhausted, and the exhaustion was certainly weighing down on her. She was alternating between feeling like her bones had melted and were sloshing around in her bloodstream and feeling like they had turned to iron and were dragging her down into the Earth. Wearily she got up and checked on everyone else; as far as she could tell they were all fine but unconscious. When she got to Magnus he woke with a start and sat up quickly, only to hang his head and squeeze his eyes shut.

"What? What is it? What's wrong?" she asked anxiously hovering over him protectively.

"Nothing. Just- agh- headache," he ground out sounding pained.

"Is there anything I can do?" she asked softly bringing her hand up to the side of his face to stroke his cheek gently and smooth out the crease that had formed between his eyebrows.

"No- ah- I don't think so," he mumbled.

"Oh!" Magnus exclaimed suddenly. "It passed," he said smiling up at Grace's concerned face. Before she could pull away and stand back up he pulled her down and kissed her lightly on the lips and then pulled away, smirking at her dazed look.

She shook her head to clear away the cobwebs in her brain and then said, "Where do you think we are?"

Magnus took a real look around for the first time and his eyes went wide when he realized where and more importantly _when _they were. "No," he muttered inaudibly, then more clearly, "No we- we can't be. It's not possible!"

"What, dear?" Grace asked looking around perhaps for threats or some kind of impending danger.

"Gracie, we're- well, we're in London," he breathed out, shock clearly etched across his tanned face. At that moment three people tumbled out of the front doors of the building; they were laughing and conversing with each other and had yet to notice the six people scattered in the courtyard. "1878 from the looks of it," Magnus finished as a beautiful boy with dark black hair and piercing eyes the color of the night sky when it still holds remnants of blue- right before the pitch black darkness consumes all else. He stopped dead in his tracks and his companions looked at him oddly before noticing what had made their friend go still.

"Magnus?" the boy questioned, obviously bewildered.

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**You know how there's a box below these words where you can type your own words in? I highly suggest doing that. Maybe you can talk about my OC, the story, if you think I should continue, your opinion, or you know what you had for breakfast or something :3**

**Seriously, though, I don't know if this warrants continuing, so tell me if you want to read more. I'm going to mark it in-progress for now...**


	2. Chapter 2

**A/N: Sorry if it seemed like I dropped off there for a while. I was debating whether or not to let you guys imagine the encounter or to just write it. I decided to just write it since this is for my friend not me!**

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Magnus, instead of answering the boy, turned to Grace. "This is kind of your fault you know," he said mildly.

"My fault?!" she asked incredulously. "You're the one who gave me the blasted thing, if it's anyone's fault it's- where is it anyway?" She whirled around in a full circle searching for the object that seemed to have brought them back to this age and place.

"Well, don't mind me!" she exclaimed sounding increasingly worried. "Go, make nice, and catch up with them. I'm going to look for the device," she said while running around the small courtyard, searching through the bushes even going so far as to start checking under the Shadowhunters who were still out cold.

Magnus shook his head at her antics and walked over to Jem, Will, and Tessa. "Hello, William," he said formally, inclining his head toward the Nephilim. "Jem, Tessa," he continued nodding at the two of them in turn.

"What- what's going on? Who are those people?" Will asked utterly flabbergasted.

"Well, Will, the unconscious people are Nephilim from New York in the 21st century. The clearly mentally disturbed girl running about-" he grinned mischievously at Grace as she shot him a venomous glare, "is an old friend of mine. Grace Lombard, she's a warlock who I've known for most of my life, though she is younger than me."

"Wait, 21st century? How is that even possible? I mean it must be true. You've popped up out of nowhere and the clothing you all are wearing…" Tessa said seeming quite confused.

"You sound like Jessamine, Tessa, talking about our clothing," Magnus responded with a teasing smile gracing his lips.

"Well," she started defensively only to be interrupted when Grace joined the conversation having given up on locating the device.

"I can't find it anywhere," Grace cried despondently. "It should be here somewhere, I know it!"

Magnus wrapped his arms around her midsection and drew her closer to his body. "Well, is it possible that it got destroyed in the Portal? It didn't seem a very stable device in the first place," he responded soothingly.

"I suppose," she muttered, still sounding put-out. "Oh, where are my manners?!" she exclaimed, "I'm Grace Lombard, High Warlock of Chicago, or I guess I will be since we don't seem to be in the proper time period. Plus, I'm thinking of moving to Manhattan, so the whole Chicago thing may indeed be inaccurate soon."

"Really?" Magnus asked his eyebrows raised in surprise. "When were you going to tell me?!"

"At the party," Grace said simply narrowing her eyes at him.

"What device?" Jem asked curiously trying to get the conversation back on track.

"It was a device that Magnus had gotten a while ago and just given to me for my birthday. It was something invented by Henry Branwell later in his life. I suppose its purpose was time travel since we were taken back in time when I got it working," she said with a thoughtful look.

"Who are the Nephilim with you?" Tessa inquired, clearly interested in them.

"The red-head is Clarissa Fray- or rather Fairchild, though she goes by Fray- and she prefers to be called Clary. The dark-haired boy is Alexander Lightwood and he goes by Alec and the dark-haired girl is his sister Isabelle," Grace was explaining when Magnus cut in. He had noticed Will, Jem, and Tessa's confused looks when the Lightwoods were mentioned.

"You cannot judge Isabelle and Alec based on your experiences with Benedict and Gabriel. They are nothing like them. In fact, the blonde boy is Jace Lightwood, Alec's parabatai. He is not a Lightwood by blood, but by choice- they are his only family- in blood he is a Herondale," Magnus interjected, carefully watching Will's reaction to this news.

Will's eyes widened comically and he opened and closed his mouth several times, seemingly at a loss for words. This was a first for William Herondale. Magnus smirked at the boy and said, "Times and people change, William. And besides, wasn't it you who started the trouble with the Lightwoods?"

"No! If she had simply chosen to transfer her affections to someone she actually had a chance with then I wouldn't have needed to embarrass her so and break Gabriel's arm!" Will defended stubbornly.

"Spoken like a true Herondale," Grace said laughing good-naturedly.

Will raised his eyebrows and looked at her questioningly before responding. "And what would you know about Herondales?"

"Well, I've come to know Jace here quite well and I associated closely with his grandmother Imogen and even knew your father, William," she said smugly, loving the shocked expression on the young man's face. She then turned to Tessa and said, "I do apologize if in the time we spend here I act like we are grand old friends. I realize that at this point in time, you've no clue who I am, but in the future we become quite close."

Tessa nodded her head, unsure of what else to do. She was still reeling from what she had just learned about the blond boy, Jace, and the time period that the Shadowhunters had come from.

"Come on, we better get them inside before they wake up," Magnus said gesturing to the four Nephilim still sprawled on the ground.

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**If there's any kind of dialogue or situation that you would like me to include here BRIEFLY, PM me or leave it in a review!**

**SO, READ AND REVIEW! Until next time,**

**Greekgirrl :)**


	3. Chapter 3

**A/N: Sorry, I'm a bit of a write-when-I-feel-like-it person. If you've been waiting, I'm terribly sorry. I hope you like the chapter though.**

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"Oh, my! What on Earth happened?" Charlotte exclaimed as she saw Magnus, Jem, Will, and Grace carrying in four unconscious people with Tessa trailing behind and trying to get Jem to let her help him carry Jace.

"Charlotte! How lovely to see you again!" Magnus replied smoothly, choosing not to answer her question.

Grace, always being the more cooperative and compassionate one, explained to Charlotte how a device had transported them all back in time and the unconscious children were future Shadowhunters. As she was talking, Alec began stirring in her arms.

"Whaa- What's going on? Where are we, Gracie?" he asked recognizing that they were clearly not in Magnus' apartment and that Grace was carrying him. Instead of answering, Grace gestured around them and Alec took in their surroundings stoically; his eyes widened fractionally when he noticed Charlotte and the other inhabitants of the London Institute, but for the most part, his expression remained unchanged.

"Okay," he muttered while rubbing his forehead, "but who are they?"

Charlotte stepped forward and introduced herself as well as the others, "I am Charlotte Branwell, head of the London Institute. The young men carrying your friends are Will Herondale and Jem Carstairs and the young lady is Tessa Gray. My husband Henry is down in the crypt working on one his inventions, doubtlessly, though you should be able to meet him at dinner."

Alec tried to stand up straight to introduce them as he was the oldest Shadowhunter of their group and had taken it upon himself to stand as acting leader. However, he was still a little out of it and drained from their trip through the Portal so he ended up falling back on Grace who tightened her hold on her dark-haired friend. "I'm Alec Lightwood. The girl that he is carrying," he gestured ambiguously in Will's general direction, "is my sister Isabelle. The other girl is Clary Fairchild, or rather Fray- either works really, but she prefers Fray, and the blond boy is my parabatai Jace Herondale. He prefers to go by Jace Lightwood, though, because we're his family," Alec explained. His speech sounded disjointed and tired, but everyone understood clearly what he was saying.

"Well, welcome to the Institute. We'll get you situated in rooms; dinner won't be held for a couple of hours, so you can rest up," Charlotte replied kindly looking at the four children with concern. Sophie soon appeared and Charlotte asked her to show them to rooms near Tessa's and Jem's so that the two could lead them to the dining room in a few hours' time. Sophie then led the way- with Jem carrying Jace, Will carrying Isabelle, and Alec and Tessa supporting Clary's lighter frame- to the rooms for the Nephilim.

"What about you two, Magnus?" Charlotte questioned looking at him and Grace curiously. "Will you be needing rooms as well?"

"No, I think we're good Charlotte. Besides, it's clear that we need to talk and figure out how to get back to our own time," he replied succinctly, grabbing Grace's hand and heading towards the library as Will, Jem, Tessa, and Sophie were returning.

Charlotte gestured for them to follow and soon enough, they were all taking seat around the roaring fire in the library.

"So, Magnus, how exactly did you all get here? I mean, Ms. Lombard here said it was a device, but what kind?" Charlotte inquired with her head cocked to the side and her intelligent eyes clouded with confusion.

"Well, I suppose that we could blame it all on Henry, but that's not very fair to him," Magnus said briefly, closing his eyes and leaning back in the wing-backed chair he was seated in. A small, humorless smile danced across his features and was gone just as quickly as it had arrived. "The main question is: how do we get back?"

"By the Angel, what's Henry done this time?" Will inquired mockingly.

"The invention was one of his, but he hasn't created it yet and it seems to have been destroyed during the journey, so that is entirely irrelevant, William," Magnus answered a bit more sharply than intended.

Will lapsed into silence as Grace looked a Magnus with concern, wondering if that headache really had passed as he was not acting like his usual carefree, happy self. She knew the happy-go-lucky face was a façade, but he didn't ever give it up as far as she had seen.

"So how do you get back?" Tessa asked curiously breaking the silence that Magnus had created.

"I honestly don't know Tessa," Magnus said wearily.

"Actually," Grace started, "I'm curious as to why you never told Magnus or me that this happened. You would have remembered and could have at least told us it was going to occur at some point. I suppose if you figure out that we are missing from our time than you can probably help us; impossible magic is rather your specialty," Grace said confidingly.

"Gracie, you know she cannot interfere with the past and you cannot tell her about her future. This sort of thing never ends well," Magnus murmured.

"I guess, but maybe she _can _help us- the Tessa from our time that is," Grace said hopefully.

"You mean I really am immortal? I'm still around in the 21st century?" Tessa asked hesitantly her eyes big and round.

"Yes, dear," Grace said smiling at her kindly, "in fact, you've been involved in Clarissa's life already and Magnus talked to you at a celebration in Idris. I wasn't there because Magnus made me promise to keep away from Idris and Alicante altogether at the time, but he told me that he talked to you."

"That's who that was?" asked a small tired-sounding voice from the doorway to the library. Grace looked up to see Clary standing there looking more awake and energized by the minute; Clary walked over to the group seated around the blazing fireplace and took one of the empty seats.

"Clary, you should be resting," Magnus said concernedly inspecting the little red-head.

"Energy rune," she said pointing to her arm and giving a crooked grin. "It works way better than those stupid energy drinks that the mundanes have. Besides, you didn't answer my question."

"Yes, that was Tessa," Magnus said resignedly. "I didn't know that you had noticed."

"Of course you didn't, I probably wouldn't have, but I was still a little jittery from everything with Jonathan and Valentine," she replied candidly. The London Shadowhunters looked vaguely confused, but no one was ready to even begin to explain Valentine and Jonathan Morgenstern to them- there was just too much horror, and no one was allowed to know too much about the future. "Anyway, anything I can do to help us get home?"

"Why would you be able to help so much?" Will asked a bit rudely.

"Would you believe me if I said that I can create new runes?" Clary responded with another question and a mischievous smirk to rival her boyfriend's.

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**And end chapter! I love just cutting it off. So, do you guys think that I should have them tell the whole stroy and just screw revealing the future or just have them explain a bit about Clary and Jace?**

**Oh, and by the way, I really like reviews! It's really strange, but it makes me feel like a good writer when I get feedback! Weird, huh?**


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